1. Field of the Invention
The present invention relates to a system and method for monitoring a conditioning catalyst for an internal combustion engine.
2. Background Art
A conditioning catalyst is a small catalytic converter positioned upstream of the oxygen sensor used for air/fuel ratio feedback control during closed loop control of an internal combustion engine. The conditioning catalyst acts as a mechanical/chemical filter of the exhaust gas. Placement upstream of the control oxygen sensor protects the sensor from contaminants while straightening the flow of exhaust gases and promoting equilibration of the engine exhaust. These features allow the main catalyst system to be used more effectively to reduce tailpipe emissions toward zero.
Because of the small size and unique formulation of the conditioning catalyst, conventional monitoring strategies may not be acceptable for various applications which require accurate monitoring to detect any reduction of conversion efficiency of the conditioning catalyst which may significantly impact the overall performance of the entire catalyst system.
An object of the present invention is to provide a system and method for monitoring a conditioning catalyst placed upstream of an exhaust gas oxygen sensor used for air/fuel ratio control.
In carrying out the above object and other objects, advantages, and features of the invention, a system and method is provided for monitoring a conditioning catalyst positioned upstream of a control exhaust gas oxygen sensor. The system and method utilize the control exhaust gas oxygen sensor for feedback control of an internal combustion engine. The system and method further utilize the control exhaust gas oxygen sensor and a monitoring exhaust gas sensor positioned upstream of the conditioning catalyst to monitor the conditioning catalyst. The method includes sampling signals generated by the control exhaust gas oxygen sensor and the monitoring exhaust gas oxygen sensor, adjusting signal samples to reduce the effect of any difference in signal amplitudes and mean values on a subsequent comparison of the signals, and comparing shapes of the signals based on the adjusted signal samples to determine operational efficiency of the conditioning catalyst.
In one embodiment according to the present invention, a system or method for monitoring a conditioning catalyst include storing signal samples from a monitoring exhaust gas oxygen sensor positioned upstream of the conditioning catalyst, and storing signal samples from a control exhaust gas oxygen sensor used for feedback control of the internal combustion engine, the control sensor being positioned downstream of the conditioning catalyst. This embodiment may include determining mean values for the monitoring exhaust gas oxygen sensor and the control exhaust as oxygen sensor, determining zero mean version of the monitoring sensor signal and the control sensor signal, summing products of corresponding values for the zero mean versions of the monitoring sensor signal and the control sensor signal, determining a product of a sum of squares of the zero mean version values of the monitoring sensor signal and a sum of squares of the zero mean version values of the control sensor signal, and calculating a ratio based on the steps of summing products and determining a product as an indication of conversion efficiency of the conditioning catalyst.
The present invention provides a number of advantages. For example, the present invention provides an efficient algorithm amenable for use in a conventional engine/vehicle controller for monitoring a conditioning catalyst based on comparison of signal shapes for a monitoring sensor and a feedback control sensor. Proper functioning of the conditioning catalyst allows the main catalyst system to be used more effectively to reduce tailpipe emissions. Accurate monitoring of the conditioning catalyst may extend its useful life and reduce premature warranty claims while promptly notifying the vehicle operator of any actual degradation in performance to comply with applicable regulations.
The above advantage and other advantages, objects, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.